As power electronic devices reach larger and larger power values and consequently emit more heat, efficient cooling of such power electronic devices becomes more and more important. One way of providing an efficient cooling system for such power electronic devices, for example semi-conductor switching elements or the like, is to provide a two-phase cooling circuit. Such a cooling circuit brings a liquid into thermal contact with the device emitting heat. The liquid is heated by the emitted heat and reaches a boiling temperature. As the temperature of the liquid itself will not rise above the boiling temperature the temperature of the liquid and therefore the temperature of the electronic device is kept at a temperature of the boiling point of the liquid as a maximum.
For example, the liquid can be stored in a reservoir inside the evaporator. The evaporator is in thermal contact with the heat emitting device. The vapor of the liquid is then converged through a conduit to a condenser. Within the condenser the vapor is changed into liquid by rejecting heat at constant temperature to a coolant fluid, air at ambient temperature for example. The vapor thus returns to its liquid phase. The condenser and the evaporator are connected via a second line in order to feed back the condensed vapor as liquid again to the liquid reservoir of the evaporator.
Such a cooling device is disclosed in U.S. Pat. No. 5,195,577. With such a cooling circuit, the evaporator provides the function of a liquid reservoir. Thus, the cross section of such an evaporator is relatively large. Consequently the efficiency of the evaporator can be relatively low. This is because of the introduced heat leads to boiling of the liquid which is provided in a large volume of the evaporator. This so-called “pool-boiling” can have poor heat transfer performance, can be bulky, can involve a large fluid inventory, and can be difficult to make leak proof at high pressure.
To address the heat transfer performance of an evaporator, it is already known to use so-called “convection-boiling”. In order to achieve the convection-boiling effect, the cross section of the evaporator can be reduced. Due to the reduction of the cross section of the evaporator, a mixture of a gas phase and the liquid phase at the exit of the evaporator flows to the condenser. By introducing the vapor mixture to the condenser with the vapor containing liquid droplets the performance of the condenser can be decreased. As such, a positive effect of reduction of the cross section area of the evaporator can be undermined to a large extent by the poor heat transfer performance of the condenser.